Thermostatic switch



Nov. 2, 1943. P. R. LEE;

THERMOSTATIG SWITCH Filed May 2. 1942 Pfiff/var l amp Ca/baaes INVENTORpau/Rbge.

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ATT'ORNEY Patented Nov. 2, 1943 2,333,536 l 'rnEnMosrA'rlo SWITCH rauln. Lee, Manssen, omo, signor a westinghonse Electric & ManufacturingCompany, East Pittsburgh, Pa., a corporation of Penn- SylvaniaApplication May 2, 1942, Serial No. 441,449. 4 Claims. '('CL 20u-122.)

My invention relates to thermostatic switching devices and moreparticularly to a thermostatic control device for the starting ofdischarge lamps, for example, sodium lamps used in street lightinginstallations.

When starting glow or discharge lamps, such as sodium lamps, used instreet lighting, it is necessary to heat the cathodes of such lamps fora minimum predetermined time, such as 30 seconde, before the lamp 1sdischarged between the anodes so as to operate or function in thedesired manner, and prolong the life oi said lamp. With the thermostaticstarting switches that are now used; in starting such lamps it isnecessary to supply sumcient internal heat in the switch structure tocause the switch to open, permitting the lamp to operate in a normalmanner. In keeping with established street lighting practice, thestarting switch must be permanently connected in series with the cathodeof the lamp in order to energize it, without the need of an attendant.Accordingly, the wattage of the heating eiemen thereof have heretoforebeen kept relatively low in order to prevent the heat therefrom fromoverheating the thermal responsive element of the thermostat. One to twominutes have, therefore, been required to start the lamp, with thethermostatic starting switches now known to the art. However, it isdesired to have the thermostatic switch connect the dischargel lamp tothe line in an operating manner within a 30 seconds time limit.

Accordingly, when using the oldl thermostats it is necessary to provideabnormally large quantities of heat thereto. To supply such anabnormally large quantity of heat to the thefmostatic switch it isnecessary to provide a relatively large ,heating element in associationtherewith inas- To overcome the operating disadvantages of thepreviously well known thermostatic switches,

`I have developed a thermostatic structure which greatly reduces thelength of time required to cause the thermostatic switch to move fromits closed or starting position, so that the sodium lamp or dischargedevice may be quickly started and which will quickly return to itsclosed position upon deenergization so as to permit the lamp to berestarted within a relatively short time, for example, 2 to l5 minutes,depending upon the ambient. f

It is therefore an object of my invention to provide a thermostaticdevice which has a relatively large heating element associated therewithfor starting a discharge lamp within the minimum time required and toprovide means associated with the heating element for causing saidelementto produce a relative small quantity of heat when the dischargelamp is in operation. e

A further object of my invention is to provide a thermostatic switchhaving a thermally responsive member, a relatively large heating elementfor actuating said thermally responsive member and a shunt for bypassinga portion of the -current ow through the device when the thermally yporting base with an auxiliary switch positioned thereupon and aninsulating member positioned between said switch and thermallyresponsive member whereby said switch is opened in response to themovements of the bimetallic element.

Yet another object of my invention is to provide a control system forstarting discharge lamps embodying a thermostatc device having a heatingelement connected in series with the lamp for actuating a thermalresponsive member and a shunting member connected in parallel with theheating element in response to the movements of the thermal memberduring the normal operation of the lamp.

Other objects of my invention will either be pointed out specifically inthe course of the following description of a device embodying myinvention, or will be apparent from such description.

In the accompanying drawing Figure l is a top plan view of athermostatic switch embodying my invention;

Fig. 2 is a sectional View taken along the line II-II of Fig. 1;

Fig. 3 is a sectional view taken along the line III-III of Fig. l; and

Fig. 4 is a schematic wiring diagram of a discharge lamp circuit havingthe thermostatic.`

switch embodying my invention associated therewith.

Referring to the accompanying drawing, I show a thermostatic switchingdevice I8 having a supporting structure I2, stationary contacts I4insulatedly attached thereto, a bimetallic thermally responsive memberI6 rigidly attached to said supporting structure and carrying movablecontacts I8 for engaging the stationary contacts, a main heating element28 for supplying a quantity of heat to actuate the thermally responsivemember, a shunting member 22 adapted to be connected in parallel withthe main heating element 28 by means of an auxiliary switch 24, and aninsulating pin 26 passing through said supporting structure I2 andengageable 4by the thermally responsive member I6 to actuate the switchin response to the movements of said thermally responsive member.

The supporting structure I2 comprises, in this instance, substantiallycircular base member I3 having sheets of insulating material 28positioned upon the lower side thereof to permit the stationary contactsI4 to be insulatedly attached to said structure. The base member I3 ispositioned within a cup-shaped sheet metal housing I5. Two terminalmembers 38 are connected to the main stationary contacts I4 to providemeans for opening or closing the main circuit. Two additional terminals32 are permanently connected to the main heating element 20 and areconnected in series with the main circuit as hereinafter described. Acentrally located aperture passes through the supporting structure forreceiving an adjusting screw 2I which rigidly supports the thermallyresponsive bimetallic member IE.

The bimetallic member I6 is, in this instance, a snap acting bimetallicdisc of 4well known design. However, it is to be understood, that saidthermally responsive member may be of any other suitable design.` Saidbimetallic element I6 has two movable contacts I8 anda third movablecontact I9 insulatedly and rigidly attacts I4 while contact I9 isadapted to engage the insulating pin 26 to move said pin and actuate theauxiliary switch 24, as hereinafter described. The bimetallic element isattached to the supporting structure by means of the calibrating oradjusting screw 2I. Said screw 2I adjusts the opening temperature of thebimetallic element by bodily moving the -central portion of thebimetallic element with respect to the supporting structure, in keepingwith es tablished practice, and is used primarily as a factoryadjustment for the thermostat.

The insulating pin 26 is formed, in this instance, of any suitableinsulating material such as a phenolic resin or a ceramic, and isslidably located within a small aperture 21 in base I3. Said pin is arelatively thin elongated member having an enlarged head portion at itslower end for preventing said pin from being moved upwardly through thesupporting structure. The enlarged head portion of insulating pin 26,when said pin is positioned within the aperture 21 in stance, anelongated spring-like movable contact carrying finger 34 which isrigidly attached to and insulated from the supporting structure by meansof one of the terminals 32. A movable contact 36 is located upon thefree end of the spring member 34 and is adapted to engage a stationarycontact 38 insulatedly attached to the supporting structure. The springcontact carrying finger 34 is positioned, in this instance, above thesupporting structure and in line with the aperture 21 so as to be'engaged by the insulated pin 26. Said spring finger 84 normally biasesthe movable contact 36 and insulating pin 26 in a downward directionwhen the bimetallic member I6 is in its closed position, see Fig. 3.Accordingly, it follows that when the bimetallic element I6 is in anopen position, the spring finger 34 moves to a lower position biasingthe insulating pin downwardly and permitting the movable contact 36 tobe in engagement with the stationary contact 38.

The main heating element 28 is positioned intermediate the supportingstructure I3 and the bimetallic element I6 and is connected at each endto the terminals 32. Said heating element 28 is designed to produce arelatively high quantty of heat in response to the flow of currentthrough the discharge lamp, which is normally 6.6 amperes. By having theheating element 28 supply such an abnormally high quantity'of heat, itfollows that the bimetallic elementwill be heated in a relatively shorttime. However, the shunting element or member 22 is connected to themain heating element 28 so as to reduce the heat output of said elementwhen the bi- -metallic element I6 has moved to its open position. Saidshunting member is, in this instance, also positioned intermediate thebase I3 and bimetallic element I6. Said shunting member 22 is controlledby the auxiliary switch 24.

It will be noted, primarily from Fig. 3, that the stationary contact 38of the auxiliary switch 24 is connected to one end of the shuntingmember 22 whereas the movable spring finger 34 is attached to one end ofa main heating element and a terminal 32. In addition, the second end ofthe shunting member 22 is connected to the other terminal 32 and to theother end of the radiant heater.

It therefore follows that when the auxiliary switch 24 is open, that iswhen the bimetallic elethe supporting structure is located intermediatement I6 is closed, the entire flow of current through the thermostaticswitch passes through the radiant heater 28. However, when the auxiliaryswitch`24 is closed in response to the movements of the bimetallicelement I6 and the insulating pin 26, the resistance or shunting member22 is connectedin parallel with the main radiant heater `28 so as toreduce the amount of current flowing therethrough.

. When operating the thermostatic switch I8 embodying my invention, andreferringto Fig. 4, the terminals 38 are connected to the anodes of thedischarge lamp while one of the cathodes of the discharge lamp isconnected to one of the terminals 32. The second cathode terminal of thesodium lamp and the second terminal 32 are then connected to the powersupply (not shown). It follows therefore that when the bimetallic memberI6 is in its closed position, whereby the auxiliary switch 24 is open,so as to disengage the shunt, the radiant heater 28 is connected lnseries with the cathodes. 'I'hen when the ra.- diant heater 28 hasincreased the temperature of the thermally responsive device I8 to itspredetermined operating value, the said bimetallic element I6 snaps toan open position, disconnecting the electrical connection between theanodes, causing a breakdown in the lamp and permitting said lamp to glowand operate in its normal manner. As the bimetallic element i6 snaps toits open position the insulating pin 26 is moved downwardly in responseto the biasing action of the spring contact finger 34 of the auxiliaryswitch 24. The auxiliary switch 24 is therefore closed connecting theshunting resistance member 22 in parallel with the radiant heater 20.Accordingly, the amount of heat produced by the radiant heater 20 isthen substantially reduced, depending upon the relative resistancebetween the radiant heater and the shunt member. The quantity of heatthen produced by the radiant heater is then merely that value necessaryto prevent the bimetallic thermally responsive member I6. from coolingto its closing temperature (substantially 175 F.)

It therefore follows that if for any reason whatsoever the dischargelamp be deenergized, the bimetallic element i6 will rapidly cool andreturn to its closed position. The amount of time normally required forsuch a closure is substantially 2 to l5 minutes depending upon theoutside ambient. Accordingly, it follows that ,the discharge lamp maytherefore be restarted within this relativel;7 short period after havingbeen deenergized.

in addition, it is obvious that have provided a thermostatic switch iol:controlling the operation of a dischargelarnp which will start said lampin a minimum length of time and will per- ,Y

mit said lamp to be restarted in a relatively short time after any powerinterruptions.

Various modifications may be made in the device embodying my inventionwithout departing from the spirit and scope thereof and I desiretherefore that only such limitationsl shall be placed thereon as areimposed by the prior art andv the appended claims.

I claim as my invention:

l. A thermostatic switch comprising a thermal responsive member movablefrom a normal position to another operating position, a heating elementfor actuating said member, a shunt, ,switch means biased toward itsclosed position and operable therein for connecting said shunt inparallel with the heating element, and means responsive to the movementof the 'thermal responsive member to its normal position for openingsaid switch, said responsive means being actuated by said biased switchmeans to permit closure thereof when said thermal responsive biasingaction when said bimetallic member is in `metallic element, a shunt,

member moves into said other of its operating positions.

2. A thermostatic switch comprising, in combination, a supportingstructure, a bimetallic element movably mounted thereon, a heatingelement for supplying an actuating heat to said biswitching means biasedtowards its closed position and operable therein for connecting saidshunt in parallel with the heating element, and a movable insulatingmember engageable by the bimetallic member for opening the switch. meansin opposition to its -a closed position.

3. A thermostatic switch comprising, in combination, a supportingstructure, a bimetallic element movablymounted thereon, a heatingelement for said bimetallic element, a shunt, switching means biasedtowards its closed position and operable therein for connecting -saidshunt in parallel with said heating element, and a movable v memberextending through said supporting structure .and adapted to looselycontact said switching means and said bimetallic element at itsrespective ends, thereby to hold said switching means in its openposition' in opposition to its biasing action when said bimetallicelement is in a closed position and to permit said switching means tooccupy its closed position when said bimetallic element moves away fromsaid switching means to its open position.

4. A thermostatic switch comprising, in combination, a supportingstructure, a bimetallic element movably mounted on one side thereof andnormally occupying a closed position near said structure, a heatingelement for said bimetallic element, a shunt, switching means biasedtowards said structure to its closed position and operable therein forconnecting said shunt in parallel with said heating element, saidswitching means being mounted on the opposite side of said structurefrom said bimetallic element, and a movable member extending throughsaid supporting structure and adapted to loosely contact said switchingmeans and said bimetallic element at its respective ends, said movablemember forcing said switching means to its open position against thebias thereof when said bimetallic element is in its closed position andsaid movable member itself being forced to follow the movement to openposition of said bimetallic element upon predetermined heating thereofby said heating element, whereby said 'switching means moves into itsclosed position.

PAUL R. LEE.

